Respiratory resistance device for use in a method of acquiring in-vivo an image of interior parts of a human body

ABSTRACT

A method of and device for acquiring in-vivo images or quantitative/qualitative data (perfusion, blood flow, vascularization, contrast enhancement, selective blood supply management) of interior parts of the human body using an imaging system includes the steps of positioning the body relatively to the imaging system, applying a respiratory resistance device to the respiratory system of the body, and performing an image acquisition step during or concomitantly an inhalation/inspiration/suction or exhalation/Valsalva/expiration phase, during which the body provides suction or exhalation against a resistance as provided by the respiratory resistance device.

FIELD OF THE INVENTION

The present invention relates to blood flow control systems, devices and methods, in particular to a respiratory resistance device for use in a method of acquiring in-vivo an image of interior parts of a human body by using an imaging system for the human body, such as x-ray and related tomographic imaging systems.

BACKGROUND OF THE INVENTION

Images of the interior of the human body are a long-established tool for providing graphic information in form of pictures, prints and screen displays for a subsequent interpretation by skilled practitioners.

For many purposes detection of blood flow related conditions is an important part of such images. In order to improve the detection of blood flow conditions it is known that injection of a contrast medium into the blood stream can add information.

A well-known example of such methods is computer tomography (CT) angiography, which is widely accepted as standard method for the examination of patients with suspected pulmonary embolism and other vascular and parenchymal diseases. The advantages of CT are obvious: it is widely available, the method is rapid, and it is highly sensitive to nodules, embolus or clots in the blood stream.

To increase the image quality of the images generated by the CT scanner, it is further known that administration of a contrast agent during the scanning process enhances the vascular compartment and other fluids in the body, usually via venous access over the upper extremity such as via the back of the hand or via an elbow vein. Alternatively, it is also known to inject contrast material in the lower extremities. It is known that the contrast-enhanced blood flows through the superior vena cava (SVC) into the right atrium, while at the same time a volume of non-contrasted blood reaches the right atrium from the inferior vena cava (IVC). Evidently, the proportion of non-contrasted blood of the IVC in relation to the contrast enhanced SVC influences the dilution of contrast medium in the right atrium/venticle, left atrium/ventricle and in the pulmonary artery (PA) and all subsequent arteries (e.g. coronary artery, carotid and brain arteries, and more distant arteries), in an effect known as transient interruption of the contrast bolus. This dilution influences potentially the diagnostic performance and quality of the entire investigation.

Several studies have been published on the effect of ventilatory activity on the blood flow as listed in the list of references below.

U.S. Pat. No. 6,631,716 suggests to set a defined volume of the lung despite respiration of a patient. No coordination of inhaling or exhaling with taking an MRI or CT is described and a contrast substance is not mentioned.

SUMMARY OF THE INVENTION

In the view of the above it is seen as an object of the invention to provide a specific dedicated device and its use, a scanning system and methods with improved and standardized flow accuracy and enhancement in the control of blood flow, dilution and enhancement properties for imaging of contrast enhanced blood flow (perfusion, first-pass enhancement, vascular supply of tumors, lesions and various tissues), particularly in relation to the vascular flow (perfusion, first-pass enhancement, arterial enhancement, improved detection of thromboembolic material within blood vessels, vascular space and supply of lesions, tumors and normal tissue) through the pulmonary artery or other arteries and veins as well as other vessels distally to the heart.

Hence, according to an aspect of the invention, there is provided a respiratory resistance device for use in a method of acquiring in-vivo an image of interior parts of a human body, wherein the method is comprising the steps of applying the respiratory resistance device to the respiratory system of the body, injecting a substance into the body and controlling or standardizing the distribution of the substance in the body through the selection of respiratory states characterized by a controlled interaction between the respiratory system of the body and the respiratory resistance device.

In another aspect, there is disclosed a method of acquiring in-vivo a series of images of interior parts of the human body, using an imaging system and including the steps of positioning a body relatively to the imaging system, applying a respiratory resistance device to the respiratory system of the body, and performing the image acquisition step during an inhalation, inspiration or suction phase, during which the body exercises suction against a resistance as provided by the respiratory resistance device. Alternatively or in addition, the image acquisition step is performed during the exhalation phase.

The imaging system can be a scanner using an x-ray imaging method, a scanner using magnetic resonance imaging or ultrasound imaging method including for example scanners for angiography, CT scanners, MR and positron emission-based variants such as PET/CT or SPECT/CT, PET/MRI or ultrasound scanners.

The respiratory resistance device includes an inner volume with an opening or openings in direction towards the physiological openings (nose, mouth) of the respiratory system of the body and essentially no openings or leaks towards the environment. The dimensions of the volume are selected such that a normal untrained patient can achieve an underpressure (in the case of suction or inspiration against resistance) or an overpressure (in the case of exhalation against resistance or Valsalva) in the inner volume of the device and, preferably, maintain such pressure for the duration of the image acquisition, e.g. preferably between 1 and 60 seconds and preferably between 5 and seconds and preferably between 5 and 30 seconds. The pressure range for such an underpressure is −8 to −20 mmHg. For overpressure a pressure range is +10 to +30 mmHg with the pressure 0 mmHg being gauged to equal atmospheric pressure.

The respiratory resistance device includes a replaceable and disposable mouthpiece to connect the inner volume of the device with the respiratory system of the body. The mouthpiece can be for example a tube or a modified tube, e.g., with an elliptical or round cross-section or with a specifically designed end for ease of use when applied to the mouth. However, in cases where it is preferred to include all openings of the respiratory system of the body, the mouthpieces can also be shaped as a mask.

It is preferred that a mouthpiece fits closely and thus tightly with the resistance device. A mouthpiece may also fit with defined spaces for the exit or entry of air between mouthpiece and resistance device.

The respiratory resistance device includes or is coupled to a sensor for measuring a parameter indicative of the pressure inside the inner volume of the device. The measurement can be displayed in a numerical form or as acoustic or optical signals or symbols, preferably indicating in operation whether the inhaling/inspiration/suction or exhaling/expiration/valsalva, respectively, is to be increased or decreased in intensity to achieve an optimal and/or steady-state pressure.

The respiratory resistance device is best operated in parallel to and in conjunction with the image acquisition of the image acquisition system and preferably also in parallel and in conjunction with an injection system for injecting of a contrast medium or other diagnostic substance into a venous vessel of the body. The device can however also be used without injection of supplementary contrast agent. If performed with contrast agent administration, it is preferred to use injection into the upper extremity or lower extremity in the case of an inhaling or suction action and injection into vessels of the lower extremity in the case of an exhaling or Valsalva action. The timings of these two or three parallel operations are chosen such that all operations are concurrently effective (well-coordinated outside and in the body) during the actual image acquisition or any other administration step.

In a variant the respiratory resistance device and the image acquisition device are linked. The link can be implemented in form of a data communication link or in form of a partial or full incorporation of the elements of the respiratory resistance device into the image acquisition system and/or injection system.

Further aspects of the invention include the respiratory resistance device, a combination of the respiratory resistance device and the image acquisition system, preferably in combination with an injection system, and any images acquired by the use of the above methods and/or devices or combination of devices and scanning systems.

The invention is particularly useful in improving the enhancement and image acquisition related to various steps of angiography of the pulmonary arteries or other arteries and veins in the rest of the body (perfusion, first-pass vascular enhancement, vascular supply of tumors, lesions and various tissues, detection of thromboembolic material).

The invention can be further used in methods and devices for administration, preferably intravenous, of a substance in order to control or standardize the distribution and/or concentration of such a substance in the body.

The respiratory resistance device of the invention can be used in general to influence via defined respiratory states the distribution and/or standardization of blood supply either from the upper, superior vena cava or lower, inferior vena cava according to the respective requirement of any medical or technical conditions such as the task to increase blood supply from the respective vessel to the right atrium of the heart or enhance the concentration of an injected substance in the blood flow in the pulmonary arteries or in vessels beyond the pulmonary arteries. This can be extended to applications such as drug injection through the upper or lower peripheral veins, invasive procedures, surgery, or any blood supply related indication.

The disclosed methods, the device, and the system according to the invention and their uses are in particular able to control and standardize blood flow to perform high contrast density within arteries and/or veins, such as pulmonary vessels, brain vessels, vessels of visceral organs or vessels of the extremities or other vessels within a human or animal body. Standardized blood flow increases contrast density in the above vessels, increasing image quality of images taken with imaging systems such as mentioned. On the other hand, the methods, devices, and systems and their use may allow to reduce the amount of contrast substances.

The above and other aspects of the present invention together with further advantageous embodiments and applications of the invention are described in further details in the following description and figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic cross-section of a respiratory resistance device in accordance with an example of the invention;

FIG. 1B is a schematic cross-section of a variant of the respiratory resistance device of FIG. 1A;

FIG. 1C shows a schematic cross-section of another simplified respiratory resistance device in accordance with an example of the invention;

FIG. 2 illustrates schematically different respiratory states during an image acquisition;

FIG. 3 is a graph of test results indicating mixing ratios between flow from the vena cave superior vs flow from the vena cava inferior depending on respiratory states; and

FIG. 4 illustrates steps in accordance with an example of the invention.

DETAILED DESCRIPTION

An exemplary respiratory resistance device 10 is shown in FIG. 1A. The device has a main body 11 of resilient material such as Teflon® or stainless steel or other similar materials. The main body provides a cap and holder for a disposable mouthpiece 12. The mouthpiece and the main body are connected to each other by a simple form fitting attachment so that the mouthpiece can be easily attached and removed from the main body by a straight insertion and extraction movement, preferably without involving a twist or use of a tool. Any similar form or attachment method might be suitable.

The mouthpiece 12 has an essentially tubular, hollow shape with a proximate opening 121 adapted for insertion into a patient's mouth and a distal opening 122 providing a flow connection into the interior of the main body 11. It should be however clear that materials, dimensions, and shapes of the main body 11 and the mouthpiece can vary widely while still maintaining the function of providing resistance against free breathing. For example, it is possible to shape the proximate opening more ergonomically or give the cross-section a more elliptical circumference. Such and similar modifications can, however, be regarded as being well within the scope of an ordinarily skilled person.

Further mounted onto the main body 11 is a pressure sensitive device 13, which can be for example a piezoresistive transducer integrated with processing circuits onto a silicon substrate. Such sensors are commercially available for example as MPXV7002 from Freescale Semiconductor Inc.

The sensor 13 is connected to a control signal generator 14. The control signal can be a numeric display of the pressure in the interior of the main body as shown. However, the control signal can alternatively or in addition be an acoustic signal or an optical signal selected according to predefined pressure thresholds or ranges. The respiratory resistance device 10 of FIG. 1 can as well omit the pressure sensitive device 13 and will work in this very simple form as well.

Thus, the control signal generator 14 can give a patient or an operator of a scanning or injection apparatus feedback on the ventilatory activity or respiratory state of the patient during the image acquisition by the scanner or during a controlled injection of a substance. The respiratory device, the methods connected therewith, and its use are able to control and standardize blood flow within patients related veins arteries during CT or Mill or other diagnostic procedures. In particular it can be indicated whether or not a patient is in the desired ventilatory activity or respiratory state or whether the patients breathing should be adapted or even changed to reach the desired state, e.g. in case of inhalation/suction whether the patient should inhale suck stronger, less strong or steady. It is for example possible to use a programmable microcontroller (not shown) as part of the control signal generator 14 so as to control a display or color-coded lights depending on the parameter as measured by the sensor 13 as feedback to patient and/or operator.

Optionally the sensor 13 can be connected to a synchronizing element 15 that is also linked to the image acquisition system. The link can be for example a wired, a wireless or an optical link for data transmission. Such an element can be used to combine information from the ventilatory or breathing activity of the patient (device) with the images acquired by any image acquisition system. This would enable a manual or automated selection of images acquired during the desired state of ventilatory activity even where this activity is fluctuating (around the desired state) during the scan. For example, the synchronizing element can include a display of pressure values along with the date and temporal information of the image acquisition. Corresponding time stamps may be included on the acquired image.

In the example of FIG. 1B the main body 11 includes a small opening 111 to the exterior to allow for a limited air flow into or from the interior and hence into or out of the patient's respiratory system. The dimensions of the opening 111 are in such a case selected so as to provide sufficient air flow resistance or restriction to prevent normal (abdominal) breathing. Small openings allowing a controlled air flow can be advantageous in order to achieve a controlled and steady state inflow of air or other respiratory gases (oxygen, xenon or other). Such an opening 111 or multiple openings may alternatively or additionally be present on the mouthpiece or may be formed by the connection means of mouthpiece and main body.

The control signal generator 14 of the example of FIG. 1B is designed as an optical indicator showing a patient in simplified symbols whether to increase or decrease the breathing efforts.

However, it is worth noting that the respiratory resistance device does not necessarily require any electronic components or any sensors to perform the function of an air flow resistance or restriction. If, for example, a simpler, more cost-efficient device is required, the main body 11 can be embodied or replaced, respectively, by a simple cap over the opening 122 of the mouthpiece as shown in FIG. 1C. If parts of the cap are designed as flexible or moveable, then the ventilatory activity can be monitored by the movement or deformation of such parts. A thin membrane in the cap or elsewhere along the tube would for example bulge in or out depending on the pressure generated by the patient during inhaling or exhaling as indicated in FIG. 1C by the dashed lines. Other examples can include a movable object or column of liquid placed in a tube and moving in dependence of the ventilatory activity of the patient. Such variants would still be sufficient to implement examples of the present invention.

The tube or mouthpiece can be adapted for use with nasal openings or with both mouth and nose. In the latter cases, it is advantageous to use a mask type connector as mouthpiece between the main body 11 of the respiratory resistance device 10 and the respiratory system of the patient instead of a tubular connector. The mask would be typically designed (e.g. with an elastic lip at its circumference) to provide sufficient air tightness to still function as a resistance against free breathing. It is further worth noting that the respiratory resistance device is not intended to provide breathing assistance during the scan as may be applied to support breathing for patients with significant respiratory failures. Thus, the known breathing masks connected to breathing support elements such as bellows or gas supply are not understood as respiratory resistance device within the meaning of the present invention.

It is further contemplated to integrate the respiratory resistance device 10 into an image acquisition system used to acquire images of the interior of the patient's body. In such a variant at least part of the main body 11, in particular the sensor 13, the control signal generator 14 and/or the synchronizing element 15 and related circuitry would be located within the housing of the image acquisition system and for example connected to the mouthpiece by means of an elongated, essentially air-tight flexible tube. Such an integration has the advantage of reducing the number of separate parts in an area which best contains only essential equipment.

In some applications, the respiratory resistance device 10 is operated typically simultaneously with the operation of the image acquisition system. The image acquisition system can be a computer tomography (CT) scanner or a magnetic resonance imaging device (MRI), Angiography, PET/CT, PET/MRI, any ultrasound imager and other similar imaging devices.

In such applications the patient is positioned within the image acquisition system with the respiratory resistance device applied to either mouth and/or nose. To enhance the contrast of any images acquired, a contrast medium, for example iodine-based contrast fluid, ultrasound contrast agent or Gadolinium based contrast material, is injected through a venous vessel of the patient. The respiratory resistance device, the methods and systems may be operated together with the injection system for injecting the contrast enhancing substance.

Details of a method of acquiring in-vivo images of the interior of a human or animal body in accordance with an example of the present invention are described in the following making reference to FIG. 2 .

In FIG. 2 there is shown a patient 20 being positioned horizontally within the tunnel of a scanner 21, which can be for example a CT scanner or an MM scanner. A respiratory resistance device 10 in accordance with an example of the invention is placed on the mouth of the patient 20. An injection system for administering a contrast fluid is connected to a venous vessel of the patient but not shown as such systems are well known in the state of the art.

The three panels of FIG. 2 illustrate three different respiratory states of the patient as can be registered by the respiratory resistance device 10. The enlarged detail shows a simplified representation of the human heart together with the blood flow through the vena cava superior SCV (entering the right atrium from above) and through the vena cava inferior ICV (entering the right atrium from below).

The respiratory states are characterized in the figure by arrows indicating predominant direction of air or blood flow or diaphragm movements including movements of the lung, respectively, on the one hand and by the meter 14 readings as displayed on the other.

The upper panel represents the basic conditions under which for example PA images are presently acquired. It is characterized herein as free breathing with no respiratory resistance device 10 in place. The air is moved into and out of the respiratory system of the human body 20 as indicated by the arrows in the area of the head. At the same time the thorax moves up and down as indicated by the arrow in the chest region of the patient 20. The breathing is typically accompanied by movement of the diaphragm as indicated by the arrows in the abdominal region of the patient 20. A flow or pressure measurement 14 shows a swing to and fro between positive or negative values (representing inflow (suction) or outflow (Valsalva) of air or a swing between underpressure or overpressure as would be measured when using the respiratory resistance device during this state of free breathing).

The respective blood flows through the ICV and SCV are as normal indicated by the two arrows of equal line thickness in the enlarged view. No change or contrast enhancement is expected in this respiratory state.

In the middle panel a respiratory state characterized as Valsalva maneuver is illustrated. In this state the patient breathes into the closed or flow restricted inner volume of the respiratory resistance device 10. The arrows in the head region indicate the direction in which the air flow is directed. The thorax moves inwards and the diaphragm upwards towards the thorax. The sensor registers this Valsalva state as overpressure typically in the range of 1 to 100 mbar for an untrained patient attempting to maintain a constant pressure for the period of the scan between 1 and 60 seconds, preferably between 5 and 45 seconds.

Again a contrast agent or any type of dye can be injected into the patient's body 20 shortly before and/or during the Valsalva state. A change from normal in the respective flows through the ICV and SCV can be observed as indicated by the arrow in the ICV being thicker than the respective arrow in the SCV. This indicates that the Valsalva state can favor the venous blood flow from the extremities of the lower body. This provides an indication that by administering a contrast medium into a venous access in a lower extremity during the image acquisition step an improved and/or more stable contrast enhancement can be achieved.

To achieve this enhancement, it can be necessary to maintain the Valsalva status during the scan acquisition and even injection or, conversely, to interrupt the scanning process during periods in which the patient exits the Valsalva state or discard or mark images obtained outside the optimal Valsalva state. For such operations the monitoring as provided by the respiratory resistance device is advantageous.

In the lower panel of FIG. 2 a respiratory state is illustrated characterized as breathing against resistance or anti-Valsalva maneuver. In this state the patient 20 sucks air from the closed or flow restricted inner volume of the respiratory resistance device 10. Again the arrows in the head region indicate the direction in which the air flow is directed. The thorax moves outwards and the diaphragm downwards towards the lower body. The sensor 14 registers this state as underpressure typically in the range of −1 to −60 mmHg for an untrained patient attempting to maintain a constant pressure for the period of the scan between 1 and 60 seconds, preferably between 5 and 45 seconds.

Again, a contrast fluid or another substance can be injected into the patient's body 20 shortly before and/or during the anti-Valsalva (suction against resistance) state. A change from normal in the respective flows through the ICV and SCV can be observed as indicated by the arrow in the SCV being thicker than the respective arrow in the ICV. This indicates that the anti-Valsalva state favors the venous blood flow from the extremities of the upper body. This provides an indication that by administering the contrast medium into a venous access in an upper extremity or a lower extremity during the image acquisition step an improved and/or more stable contrast enhancement can be achieved. To achieve this enhancement it can be necessary to maintain the anti-Valsalva state for the duration of the scan or, conversely, to interrupt the scanning process during periods in which the patient exits the anti-Valsalva state or discard or mark images obtained outside the anti-Valsalva state. Again, the presence or absence of such states is enabled and monitored by the respiratory resistance device 10.

Test results using various standardized breathing states or maneuvers and flow-sensitive MR phase contrast techniques in the SVC and IVC and imaged in the supine position on a 1.5 Tesla MRI unit (Achieva 1.5 T, Phillips Healthcare, Best, The Netherlands) are shown in FIG. 3 using an 8-channel torso coil (Philips Health care) covering the entire chest allowing the regular acquisition of two sets of heart triggered dynamic phase contrast (PC) images (TR 50 msec and TE 4 msec; Slice thickness 8 mm, flip angle 15°, velocity encoding 100 msec; voxel size 1.9×2.5) in the axial section of the SVC and IVC.

In order to guarantee standardized and reproducible breathing an MR-compatible respiratory resistance device was used for controlling and monitoring the respiratory pressure and blood flow during the entire maneuvre. Besides the newly defined breathing method “suction against resistance”, previously defined techniques such as valsalva, apnea after end of inspiration, apnea after end of expiration and free breathing are also investigated allowing comparison with known studies (see references).

The capital letters in FIG. 3 indicate the respiratory state or the interaction with the respiratory resistance device, where used. IVC/SVC ratios for stroke volumes (white boxes) and flux (grey boxes) are shown for free breathing (A), end of inspiration position with breath hold (B), end of expiration position with breath hold (C), Valsalva maneuver at +10 mm Hg (D), Valsalva maneuver at +20 mm Hg (E), Valsalva maneuver at +30 mm Hg (F), suction maneuver at −10 mm Hg (G), similar suction maneuver at −20 mm Hg (H). Boxes show the median and the 25th and 75th quartiles; whiskers show minimum and maximum values. The optimal ratio is achieved in the suction mode with thoracic underpressure, but standard deviations are higher, demonstrating more unstable conditions. Other states such as the Valsalva maneuver can be considered, too, but show a much-reduced effect under these circumstances.

It should be noted that the method and respiratory device as described in the example using an Mill scanner above may work equally well or even better in connection with a CT scanner or other imaging or diagnostic techniques.

The steps performed on a patient are summarized in the flow chart of FIG. 4 . However, it should be noted that the sequence of steps as shown in FIG. 4 is not indicative of a specific temporal order of such steps as most of the steps are best undertaken simultaneously to achieve the better results.

It should be noted that the above methods and devices can be used in any method requiring control or standardization of the mixing of the flow of blood from the IVC and SVC, and can be effective even in the blood circulation beyond the pulmonary arteries and the lungs, e.g., into the peripheral organs and body parts. Such a control and standardization can enable for example the improved performance of first pass measurements or perfusion, particularly for tumors or other vessels and tissues, or the distribution of drugs or dyes into the body, particularly where such drugs or dyes are administered intravenously.

When used with a contrast medium suited for ultrasound acquisition system, such as gas bubbles, the above methods and devices can also be applied to image acquisitions using an ultrasound scanner.

While there are shown and described presently preferred embodiments of the invention, it is to be understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims. 

1. A respiratory resistance device for use in a method of acquiring in-vivo an image of interior parts of a human body of a patient, the respiratory resistance device comprising: a main body with one or more openings to connect in use with a respiratory system of the human body; an inner volume defined by the main body, the inner volume being in fluid communication with the one or more openings of the main body and closed to an environment; a replaceable subpart connectable with the main body, the replaceable subpart comprising a mouthpiece, wherein the mouthpiece is in fluid communication with the one or more openings of the main body when the replaceable subpart is connected with the main body, wherein an overpressure of +10 mmHg to +30 mmHg is generated in the inner volume of the main body during an exhalation of the patient into the mouthpiece while the respiratory resistance device is connected with the respiratory system of the human body so that the closed inner volume of the main body is blocking partially the flow of air out of the respiratory system of the human body during exhalation of the patient, and an underpressure of −8 mmHg to −20 mmHg is generated in the inner volume of the main body during an inhalation of the patient from the mouthpiece, while the respiratory resistance device is connected with the respiratory system of the human body so that the closed inner volume of the main body is blocking partially the flow of air into the respiratory system of the human body during inhalation of the patient, wherein the main body comprises a sensor for measuring a parameter related to the pressure in the inner volume of the main body, and wherein the respiratory resistance device further comprises a control signal generator for generating a control signal indicative of a deviation from a predefined pressure range of the underpressure or overpressure in the inner volume of the main body during inhalation or exhalation of the patient from or into the mouthpiece, respectively.
 2. The respiratory resistance device according to claim 1, wherein the inner volume of the main body is dimensioned to generate an overpressure of +10 mmHg to +30 mmHg in the inner volume during an exhalation of the patient into the mouthpiece under normal exhalation conditions of a human respiratory system and an underpressure of −8 mmHg to −20 mmHg in the inner volume during an inhalation of the patient from the mouthpiece under normal inhalation conditions of a human respiratory system.
 3. The respiratory resistance device according to claim 1, wherein the sensor is in communication with the control signal generator to generate the control signal indicative of a deviation from an optimal inhalation or exhalation state of the respiratory system of the patient during inhalation or exhalation of the patient from or into the mouthpiece, respectively.
 4. The respiratory resistance device according to claim 1, wherein the control signal generator includes an indicator indicating whether the pressure in the inner volume is lower than a preset lower limit or higher than a preset upper limit.
 5. The respiratory resistance device according to claim 1, wherein the replaceable subpart comprises a tube acting as a mouthpiece to be in fluid communication with a mouth of the patient.
 6. The respiratory resistance device according to claim 1, wherein the control signal generated by the control signal generator is an acoustic or optical signal.
 7. The respiratory resistance device according to claim 1, wherein the sensor is a piezoresistive transducer.
 8. A system for acquiring in-vivo an image of interior parts of a human body of a patient, the system comprising: an image acquisition system; an injection system configured to intravenously inject a substance selected from a contrast fluid, a dye and a drug into the human body; and the respiratory resistance device according to claim 1, wherein the image acquisition system is configured to acquire an image of inner parts of the human body during at least one of an inhalation phase during which the human body provides suction against a respiratory resistance provided by the respiratory resistance device, and an exhalation phase during which the body provides exhalation against a respiratory resistance provided by the respiratory resistance device.
 9. The system according to claim 8, wherein the image acquisition system and the respiratory resistance device are linked with each other by a data communication link.
 10. The system according to claim 8, wherein the sensor of the respiratory resistance device is linked to a synchronizing element which is linked to the image acquisition system.
 11. The system according to claim 8, wherein the respiratory resistance device is operated simultaneously and synchronized with the operation of the image acquisition system.
 12. An image enhancement kit comprising a contrast agent substance for injection into a human body and the respiratory resistance device according to claim
 1. 13. A respiratory resistance device for use in a method of acquiring in-vivo an image of interior parts of a human body of a patient, the respiratory resistance device comprising: a main body with one or more openings to connect in use with a respiratory system of the human body; an inner volume defined by the main body, the inner volume being in fluid communication with the one or more openings of the main body and closed to an environment; a replaceable subpart connectable with the main body, the replaceable subpart consisting of a mouthpiece, wherein the mouthpiece is in fluid communication with the one or more openings of the main body when the replaceable subpart is connected with the main body, wherein an overpressure of +10 mmHg to +30 mmHg is generated in the inner volume of the main body during an exhalation of the patient into the mouthpiece while the respiratory resistance device is connected with the respiratory system of the human body so that the closed inner volume of the main body is blocking partially the flow of air out of the respiratory system of the human body during exhalation of the patient, and an underpressure of −8 mmHg to −20 mmHg is generated in the inner volume of the main body during an inhalation of the patient from the mouthpiece, while the respiratory resistance device is connected with the respiratory system of the human body so that the closed inner volume of the main body is blocking partially the flow of air into the respiratory system of the human body during inhalation of the patient, wherein the main body comprises a sensor for measuring a parameter related to the pressure in the inner volume of the main body, and wherein the respiratory resistance device further comprises a control signal generator for generating a control signal indicative of a deviation from a predefined pressure range of the underpressure or overpressure in the inner volume of the main body during inhalation or exhalation of the patient from or into the mouthpiece, respectively. 